A technique for utilising peripheral pressure pulses to determine the pulse waveform at other body sites, particularly the ascending aortic waveform, is disclosed in U.S. Pat. No. 5,265,011 by Michael F. O'Rourke. The books "The Arterial Pulse" by O'Rourke, Kelly and Avolio published by Lea Febiger, Philadelphia USA 1992 and "Arterial Vasodilation", by O'Rourke, Saffer, and Dzau, published by Arnold, London 1993 disclose the use of a measured peripheral waveform to determine the waveform at another site, using an empirically determined transfer function. The derived waveform can be calibrated, as it is derived from the peripheral waveform which itself is calibrated. In these documents, it is assumed that the brachial cuff sphygmomanometer measurement can be used to directly calibrate waveforms measured at the radial artery. It is assumed that relatively little change occurs in the parameters between the brachial artery and the radial artery. Whilst this is a reasonable working assumption, it is not strictly accurate.
It is an object of the present invention to provide an improved calibration procedure, such that derived waveforms are able to be more accurately calibrated.